Color television screen



Dec- 1, 1959 E. A. LEDERER 2,915,661

COLOR TELEVISION SCREEN Filed Feb. 19. 195:5

INVENTOR WITNESSES:

9/4 AL-7 7 Ernest A; Le'derer. QM/QM f g m ATTORNEY United States PatentCOLOR TELEVISION SCREEN Ernest A. Lederer, Essex Fells, N.J., assignorto Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application February 19, 1953, Serial No.337,710

1 Claim. (Cl. 313-73) My invention relates to color television receiversand in particular relates to a new type of kinescope embodying a novelelectron phosphor screen for reproducing television images in color.

Practically the only color television system today that has been provedreally successful in reproducing high grade pictures employs a kinescopewhich projects a cathode ray beam through fine holes in a mask-plateonto dots of red-emitting, green-emitting and blue-emitting phosphordistributed in a precisely-spaced aray on the viewing screen. Thisrequires a tolerance of less than $00015 inch in positioning the maskand the dots, which can be attained in factory production only at theexpense of very costly rejects and shrinkage.

Such precise tolerances are inevitable in any colorreproduction systemwhich relies on positioning to attain color-separation in reproduction,so that a change of approach to solution of the problem is necessary. Mysystem effects this change by resorting to electric potentials todetermine the color of the light being emitted by the screen phosphorsat any instant, and this general method probably offers the idealapproach to a practicable solution. The kinescope screen would probablybe in many respects almost indistinguishable in geometry from those ofpresent black-and-white picture tubes and should require no greaterprecision in manufacture than do the latter.

There are strong reasons for thinking that it will'be possibleultimately to produce phosphors containing in the same crystal differentactivators which will make the color of the phosphor a function of theenergy of the electrons in the beam impinging on the phosphors-of thereproducing screen. Development of such phosphors which will betechnically satisfactory may, however, require several years offundamental research. My present disclosure relates to two expedientswhich may be shortcuts to the same goal. One possibility lies in makingthe particle size of the phosphor very small, mixing with a suitablebinder such as nitrocellulose, and extruding the resulting paste intofilaments of diameter of the order of five to ten mils. Three suchfilaments, respectively composed of a redemitting, a green-emitting anda blue-emitting phosphor, are continuously pushed through a suitabledie.

One object of my invention is to provide a new and improved system forproducing color television pictures.

Another object is to produce a new and improved kinescope for colorpicture reproduction purposes.

Another object is to provide new and improved methods of producing tubessuitable for reproducing pictures in color.

Another object is to provide an improved type of color picturereproduction which employs irradiation of the screen with auxiliaryradiation from a source local to the receiver to increase the brightnessat which the emitters of certain colors radiate light when signals ofcorresponding color are arriving at the picture screen.

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Yet another object is to employ screens in which electroluminescentphosphors are stimulated by signals of a particular color to emit lightof that color with increased brightness when they arrive at thereceiver.

Another object is to provide a novel structure for color-picturereproducing tubes.

Still another object is to provide color picture reproducing screens ofa novel type.

Yet another object is to provide a novel method for producing phosphorscreens which are controllable in color in response to electricpotential effects.

Other objects of my invention will be evident to those skilled in theart on reading the following description taken in connection with thedrawings, in which:

Figure 1 is a view in perspective of a component of my improved phosphorscreen at an intermediate point in its process of manufacture;

Fig. 2 is a similar view of the subject matter of Fig. 1 at a secondstage of the process of manufacturing it;

Fig. 3 is a similar view of the same component at a still more advancedstage of the process;

Fig. 4 is a view in perspective illustrating one step in a differentprocess of manufacturing components for a phosphor screen in accordancewith my invention;

Fig. 5 is a similar view illustrating the component initially shown inFig. 4 at a yet more advanced stage in the manufacture;

Fig. 6 is a detailed view of a kinescope screen employing my invention;and

Fig. 7 illustrates a kinescope employing a screen according to myinvention.

Referring in detail to Figs. 1, 2 and 3, particles of three differentphosphors which respectively emit red, green and blue light are made upwith a fineness of five to ten mils. This may be done in any way knownto those skilled in the art, for example by grinding and sieving. Thered-emitter may, for instance, be rhombic Zn (PO.,) :Mn, thegreen-emitter may be ZnSiO :Mn, and the blue-emitter may be a mixture of50% CaMg(SiO :Ti and 50% Cubic ZnSzAg. The energy required in anincident electron to excite light of a given intensity in a givenphosphor may be varied by mixing with the phosphor certain materialssuch as thoria or silica or other refractory substances. Thus it ispossible to control the light intensity which the respective phosphorsare caused to emit by an electron beam having a given acceleratingvoltage, maintaining thelight intensity of, say, the green and bluephosphors low and exciting the red phosphor to full intensity by givingthe screen a lower potential relative to the electron gun; fullyexciting the green when desired by giving the screen an intermediatepotential; and fully exciting the blue phosphor only when a highpotential is given the screen. The accelerating voltage or electronenergy may be modified by varying the potential between the cathode ofthe electron gun and the screen, thereby determining the excitation ofselected phosphors. The video intelligence may be impressed on thecontrol grid of the electron gun and thus the intensity of the electronbeam is controlled by varying the number of electrons.

Corresponding with the above principle, the greenemitting phosphorpowder is admixed, for example, with finely divided silica, let us say,having a particle diameter of from 3 to 5 microns in the amount of about5 to 10 percent by weight; and the blue-emitting phosphor powder isadmixed with thoria of about 3 to 5 microns particle diameter in theamount of about 10 to 20 percent dies to produce three filaments ofsubstantially circular or other suitable section of about to mils indiameter which are then combined as indicated in Fig. 1. One way ofcombining the three filaments as shown would be to use a die with threeoutlets positioned asshown by the circular filament ends in Fig. l, therespective outlets communicating with separate, containers of the threemixes of phosphor and binder.

The trefoil filament 1, 2, 3 of Fig. 1 may then be coated with more ofthe binder and passed through a second die having a circular outlet ofarea slightly greater than the aggregate area of the three componentfilaments, from which it will emerge with a cross-section like thatshown in Fig. 2. The filament 4 together with its coating of binder isthin, having a diameter of twenty to twentyfive mils, for example, andis sliced in a microtome to a thickness of about one to three mils toform flat pellets 5 such as appear in Fig. 3.

A large number of these pellets are then settled, through water or othersuitable liquid vehicle, on the face of the glass screen for a picturetube. The pellets will settle fiat against the screen face forming asufiiciently uniform layer of thickness determined by the length of thesettling period. The layer may then be dried and the binder removed byheating to a temperature of around 150 to 200 C. Use of phosphors havingdifierent excitation threshold may supplement the addition of inertpowders as a means of differentiating the excitation voltages to whichthe respective colors respond.

As an alternative to admixing silica or other powders with thephosphors, filaments comprising simply the respective color-emittingphosphors and nitrocellulose binder may be extruded, as described above,and the filaments then coated by dipping or dragging the filamentthrough a suspension of silica or other refractory powder abovedescribed in water or other suitable vehicle. Alternatively, gaseouscompounds of silicon or thorium may be used to deposit silica or thoriafrom the gaseous phase on such filaments.

Where filaments thus coated are used, the arrangements shown in Figs. 4and 5 may be used to produce pellets for deposition on the screen. Thusred-emitting, greenemitting and blue-emitting phosphor filaments 6, 7, 8coated as just described are passed through rolls 9, 11 in contact witha strip 12 of nitrocellulose to which they are attached by mere pressureor by additional binder. The strip 12 is then sliced into little rods orpellets by the microtome, producing a unit 13 illustrated in Fig. 5. Theunits 13 could be settled through liquid as previously described inconnection with those of Fig. 3, or electrophoretic methods might beused to insure their flat deposition on a glass surface coated with athin transparent coating made from tin chloride in ways well known inthe electronics art.

Electrophoretic methods of depositing finely divided materials aredescribed in an article by Troelstra Applying Coatings byElectrophoresis, Philips Technical Review, April 1951, page 293. Ingeneral, a transparently thin conductive coating of any well-known typeis deposited on the surface to be covered with phosphor; the screen isthen placed in contact with a water or other liquid suspension of thephosphor or other particles to be laid down; and an electric fieldimpressed normal to the conducting surface until a coating of thedesired thickness of the suspended particles accumulates;

Another arrangement by which the different coloremitting phosphors maybe successively excited to intense luminosity in correspondence withthecolor signals being transmitted to a color television receiver may bemade up as follows. There are numerous phosphors known in the art whichemit light of much greater intensity when they are irradiated withinfrared rays or some other type of radiation at the same time anelectron beam is incident upon them. The phosphors ZnSiO :Mn and 50%CaMg(SiO :Ti and 50% cubic ZnSzAg, referred to above as producingrespectively green light and blue light under electron bombardment,might be mentioned as among these. f

In accordance with the general principles of this modification of myinvention, particles or rods formed in the way'already described anddeposited on glass to form screens are stimulated not only by electronbombardment from the cathode ray beam in the kinescope but are alsoirradiated at the proper times by such stimulating radiations asultraviolet light and soft X-rays, or whatever other radiations may bemost desirable stimulators. Thus, in operating such a system, theauxiliary radiation would be shut off so that the electron beam alonebombarded the screen when a red color signal was being transmitted tothe receiver; then when the green color signal arrived, the infraredradiation, let us say, would be turned on to irradiate the screen inaddition to the cathode ray beam; and when the blue picture signal beganto come in, the other type of radiation would be turned on in place ofthe infrared radiation, the electron bombardments by the cathode raybeam still continuing. When found desirable, the intensity of thecathode ray beam could be altered coincidently with the turning on ofeither of the auxiliary radiations where such a procedure increased thecolor effectiveness of the screen.

Still another expedient for emphasizing the color emission of one of thephosphors, when desired, is to be found in the phenomenon ofelectroluminescence in which certain substances, notably cadmium sulfideand properly processed zinc sulfide and silicon carbide, are renderedluminous by a rapidly varying electric field traversing their particles.The brightness of light at any instant in the case of electroluminescentmaterials is approximately proportional to the rate of change of voltagegradient. Arrangement making use of this phenomenon in certain types ofimage intensifier tubes are described and claimed in application SerialNo. 283,094 of Everet W. Vaughn et al., filed April 18, 1952, for aFluoroscopic Image Tube, and assigned to the assignee of thisapplication.

In Fig. 6 is shown a detailed view in cross section of a portion of thepicture screen of a kinescope arranged for use of the auxiliary lightstimulation procedure just described. Thus a glass screen 21 isprovided, in the manner described in connection with Figs. 1 through 5,with a layer of pellets 22, 23, 24 respectively comprising a red-emittersuch as rhombic Zn (PO.,) :Mn, a greenemitter such as zincsilicate:manganese (ZnSiO :Mn) and a blue-emitter such as 50% CaMg(SiO:Ti and 50% cubic ZnSzAg. The surface of the glass screen 21 on whichsuch pellets rest is preferably coated with a thin layer 25 oftransparent conducting material such as NESA, a transparent glassmarketed by the Pittsburgh Plate Glass Co. of Pittsburgh, Pa. The outersurface of the pellets is likewise coated with a transparent layer 26 ofsome conductive material such as nickel, gold, silver or the conductiveglass NESA sold by the Pittsburgh Plate Glass Co. of Pittsburgh, Pa.,which may, for example, be deposited by evaporation in vacuo onto acollodion film formed as described in the application Serial No. 264,196of Richard L. Longini and Donald L. Coles filed December 29, 1951 for aHeat Sensitive Element, now US. Patent 2,727,118 issued December 13,1955 and assigned to the same assignee as the present invention. Theconducting layers 25 and 26 are connected to inleads 28 and 27,respectively, upon which an electric gradient may be impressed at willfrom a variable voltage source 29.

Fig. 7 shows a kinescope of conventional type provided with a screensuch as that described in Fig. 6. The conductive layers of the screenare provided with inleads 27 and 28 connecting them through anelectronic switch 31 which may be of the type described in an articleentitled A 45-Degree Reflection Type Color Kinescope, page 1201 ofOctober 1951, Proceedings of the Institute of Radio Engineers publishedby the I.R.E., New York City, by which a voltage from a suitable source32 may be impressed between said conducting layers at periodic intervalscorresponding to the transmission of blue picture elements. Theenclosure of the kinescope in Fig. 7 is likewise provided with a sourceof ultra-violet light 33 which may be turned on and ofiby an electronicswitch 34 in synchronism with the transmission of the blue lightpictures and which is positioned to irradiate the screen.

The kinescope is provided with a conventional electron gun system 35 forscanning in the usual way the phosphor layer of its picture screen 21.With the abovedescribed arrangement, the electron beam bombards thescreen but the auxiliary radiation source 33 and voltage source 32 areturned off when a red light picture signal comes into the receiver. Thenwhen a green light signal comes in, the voltage of electroluminescencestimulator 32 is turned on so that the electron beam will produce anintense luminosity from any one of the pellets on the picture screenwhich emits green light and on which it is incident at the time. Thenwhen the blue picture signal comes in, the electroluminescence generator32 is turned ofi and the ultra-violet source 33 is turned on therebycausing the blue-emitting pellets on the screen to flash into highintensity while the red-emitting and greenemitting pellets on which theelectron beam is incident, are less than intensely luminous.

Excitation of such stimulations respectively of the red-emitting, thegreen-emitting and the blue-emitting phosphors on the screen thus insynchronism with the incoming color signals of the picture willstimulate light of the proper color to correspond point byv point overthe surface of the screen as the scanning operation lays down thepicture. Electron switches and their control circuits suitable forenergizing the auxiliary radiation sources in synchronism with incomingpicture signals are well known in the art of color television today. To

give one instance, the October 1951 I.R.E. Proceedings, above-mentioned,describes such switching and control arrangements for color television.

The above-described system may be adapted to both frame sequential anddot sequence types of transmission as will be readily apparent to menskilled in the color television art.

I claim as my invention:

A color-picture receiver comprising means for projecting a scanning beaminto incidence upon a picture screen, said screen comprising elementalareas which emit lights of difierent colors at the point of incidence ofsaid beam, conducting sheaths sandwiching said elemental areas, meaus tosuliuse said screen with radiation of a predetermined wave length, andleads for impressing a variable electrical gradient between saidsheaths.

References Cited in the file of this patent UNITED STATES PATENTS2,239,887 Ferrant Apr. 29, 1941 2,286,478 Farnsworth June 16, 19422,287,308 Herbst June 23, 1942 2,337,569 Pritchack Dec. 28, 19432,372,903 Lynch Apr. 3, 1945 2,413,459 Lynch Dec. 31, 1946 2,493,200Land Jan. 3, 1950 2,543,477 Sziklai et al Feb. 27, 1951 2,545,420Sziklai Mar. 13, 1951 2,566,713 Zworykin Sept. 4, 1951 2,580,073 BurtonDec. 25, 1951 2,598,504 Carlson May 17, 1952 2,635,203 Pakswer Apr. 14,1953 2,728,025 Weimer Dec. 20, 1955 2,728,870 Gungle et al. Dec. 27,1955 2,730,644 Michlin Jan. 10, 1956 2,768,318 Bradley et a1. Oct. 23,1956 2,778,971 Sunstein Jan. 22, 1957 OTHER REFERENCES DeMent:Fluorochemistry, Chemical Pub. Co., Inc., New York, 1945, pages 295 to297.

Garlick: Luminescent Materials, Oxford at the Claren-

